This invention relates to electrodes and, more specifically, to a zircalloy tipped electrode for an electrochemical corrosion potential (ECP) sensor.
Existing ECP sensors consist of a platinum tipped sensor, a zirconia ceramic tipped sensor or a stainless steel tipped sensor. The platinum type sensor is used as a standard hydrogen type electrode. This serves as the reference electrode since it has a typical Nernstian response to the hydrogen concentrations in the reactor water. A platinum tipped ECP electrode is disclosed in commonly owned U.S. Pat. No. 6,222,307. Another commonly. owned patent, U.S. Pat. No. 5,192,414, discloses stainless steel or platinum tipped ECP electrodes.
The zirconia ceramic type sensor is a ceramic ECP electrode that contains a metal-metal oxide mixture inside the permeable zirconia ceramic tip. See, for example, commonly owned U.S. Pat. Nos. 5,043,053 and 6,357,284. This type of electrode responds to the oxygen concentrations in the reactor water. The measurement obtained with the zirconia ECP sensors is a raw voltage representing the oxygen concentration and electrical potential of the reactor water. These measurements must be processed through a data acquisition system so that calculations can be performed to obtain concentrations xe2x80x9ccorrectedxe2x80x9d to the standard hydrogen electrode scale, which can then be correlated to the corrosion potential of specific surfaces exposed to the reactor water.
The stainless steel electrode is used as a comparative measurement device. The potential measured by this electrode is compared to that of the platinum standard and zirconia ceramic reference electrodes, thus allowing the ECP of the stainless steel surface in a given water chemistry to be directly measured. It would be advantageous to have a similar electrode designed to incorporate a metal tip made of zircalloy instead of stainless steel. This would allow the ECP of zircalloy to be directly measured as compared to the potentials measured by the standard hydrogen and reference zirconia electrodes.
The ECP electrode in accordance with the invention includes a metal electrode tip that is closed at one end. The electrode tip is manufactured from zircalloy metal and is used in calculating the electrochemical corrosion potential of zircalloy metal exposed to reactor water through comparison to a standard reference platinum electrode. The zircalloy metal electrode tip is brazed to a ceramic insulator which is, in turn, brazed to an iron-nickel alloy adapter sleeve having a coefficient of thermal expansion which closely matches that of the ceramic insulator. The adapter sleeve is welded to a metal adapter housing, which is in turn secured to a metal coaxial cable. The coaxial cable carries. the electrical signal from the electrode tip to a data acquisition system.
Accordingly, the present invention relates to an ECP sensor electrode comprising an electrode tip, having a closed end and an open end, the open end secured to a ceramic insulator, with a conductor wire extending through the insulator into the electrode tip, and wherein the electrode tip is constructed of zircalloy.
In another aspect, the invention relates to an ECP sensor electrode comprising a zircalloy electrode tip having a closed end and an open end, the open end secured to a ceramic insulator, and a conductor wire extending through the insulator into the electrode tip; wherein the open end is brazed to one end of the ceramic insulator; and an opposite end of the ceramic insulator is brazed to one end of a substantially cylindrical metal adapter sleeve; wherein an opposite end of the metal adapter sleeve is secured to an adapter housing supporting a coaxial cable connected to the conductor wire.